Howto: KVM Server Virtualization

by Dagorret Carlos ·
Published December 26, 2012
· Updated December 26, 2012

I want to virtualize a server from scratch. I have a server in mind already, but I don’t want to bother with virtualizing it directly since it is running on a dated OS. I figure I will build a new VM in parallel on some spare hardware and then migrate the image over to my beast server. Some key benefits of this are that I can use some of the spare capacity of that beast server to test out other server operating systems and software in parallel with my main server. Also, I can install crashplan on the host itself and have it backup my server images for painless offsite backup whereas now I really don’t have a backup of the physical server configs.This guide will be devided into three stages as follows because this is the order I carried out the steps in.

Set up a host CENTOS 6.3 server

Set up a guest MINT 14 server (with MATE desktop)

Set up a static bridged network and configure our VM to use it

Setting up host server

First thing, you should make sure your processor supports kvm virtualization. Install CENTOS 6.3 or later. I am not a redhat/centos guy for most of my home Linux systems, but it seems ideal for a VM host where I don’t really need the latest and greatest packages and stability and concise configuration are key. I am assuming you can install this on your own with the graphical installer or however.

Now, we will need some special tools to get virtualization running. As root, do the following on your fresh CENTOS box:

# I ran into this not being on. The virt-manager just sat there trying to connect before I did this.

service libvirtd start

chkconfig libvirtd on

That’s it, you are ready to virtualize! Some people say you need to deactivate SELINUX, but some say it isn’t needed. You can do so by editing /etc/selinux/config if you think it is causing you troubles.

Setting up a guest server

This is pretty straight forward (except for the last little bit where we correct some video settings). Download an ISO and/or burn it to a CD for the OS you want to install. In this example, I am using Linux Mint 14 with MATE desktop.

Open up the KVM manager tool you installed in step 1.

In the top left click play button on a monitor that says “Create a new virtual machine” when you hover over it. Then, on the step 1 window name your server and pick ISO/CDROM.

On the step 2 windows, tell it where the ISO/CD is. For OS type, just use Linux. For version, go to “see all” and select the latest kernel available as shown. The OS being installed is so far ahead (3.x) kernel, that there is no more up-to-date choice that I can tell.

On the step 3 window, set up your memory (give Mint 14 at least a gig) and select how many cores to set. There are ways to alter this later if you need to, so don’t get too hung up on getting this just right now. In my case, the host has too few cores and too little memory to set it up like I will after I migrate it to something more powerful.

On the step 4 window, set up your storage. The default 8GB is probably a bit tight, 20GB+ may be better. After taking this screenshot, I chose 40GB. You don’t have to “allocate entire disk now.” I say let it grow dynamically.

On the step 5 window, review your selections and then hit finish. If you carried out the final section of this guide before doing the VM setup, you could expand the Advanced options and choose your network now. However, I am trying to break this into quick chunks for time-crunched people like myself and getting your VM up feels like progress ;-).

Now launch your VM and install the OS as you would on a physical machine (except maybe more slowly and less responsively) in the window that pops up. The blue “i” icon on the VM popup window (next to the terminal icon) will show you system stats and you can change things here.

I had an issue where every time I logged in, I got bounced back out. To fix it, I had to do two things. I did these out of order, so I don’t know if they were both necessary. I will share them in the opposite order I did them. If the first step works for you, don’t bother with the second.

First, switch the virtual video adapter from cirrus to vga.

If you still can’t login to the VM gui, then carry out this second part. At the login screen to your guest OS:

use the send menu to send ctrl alt f2 # to drop to virtual terminal on VM

login as root

apt-get install nvidia-current

reboot

After it reboots, it should work like a charm. Also, if you want to shut off the GUI later, you can always edit the /etc/inittab to prevent loading the GUI. I like having the option of the GUI on my servers since it really doesn’t take up that much disk space and can be disabled as needed.

Your network should be set up fine for using this guest VM like a desktop to go on the internet, get updates, etc as long as your host’s network is working right. Out of the box it gives you a virtual network using NAT which is fine for these purposes. I could reach out to other boxes on my network just fine. The show-stopper for virtualizing a server, is that nothing else on my network can reach out to the VM except its own host. In the next step, we fix that nonsense.

Setting up a bridged network

Okay, this was a bit foreign to me. I have used a wireless network bridge, but I never built a virtual bridge on a box off of a physical NIC before. I am doing something odd here in using a static IP for the bridge itself which nobody seemed to do in their guides, but it is easy enough.

I have to give some credit here as I got started with bridging using information from this site. I also found a good reference on killing NetworkManager which doesn’t play nice with your bridge. Anyway, here is my condensed version.

As root on the host:

service NetworkManager stop

chkconfig NetworkManager off

chkconfig network on

Clear out any crappy config files you have like /etc/sysconfig/network-scripts/ifcfg-Auto_eth0 that were made by NetworkManager.

vi /etc/syconfig/network-scripts/ifcfg-eth0 #(this may be different on your system if eth0 isn’t your NIC)

Now you need to edit your VM settings. While the VM is off, open it and hit the blue “i” like we did to alter the video adapter. I used device model vertio because it was the default, but there may be merit in some of the other options. Anyway, go to the NIC device and set it up as shown:

Then click apply. Now you can boot up the guest OS and configure its network settings with a normal static IP or even DHCP. It will work just like it is on the network directly using its own NIC.I hope this guide has been helpful for you. Feel free to offer any tips or improvements or ask questions. Now go forth and virtualize!